The present invention relates to stinging cells or capsules and to the use thereof in compositions, devices and methods for delivering a therapeutic, cosmetic or diagnostic agent into a tissue. More particularly, the present invention relates to the use of stinging cells or capsules as transdermal/intradermal, transmembranal or transcuticular delivery devices.
Therapeutic agents such as drugs are a mainstay of modern medicine and are used for the prevention, diagnosis, alleviation, treatment, or cure of diseases.
Biological, biochemical and/or physical barriers often limit delivery of therapeutic agents to target tissue. For example, skin and/or various organ membranes are physical barriers, which must be traversed by a topically administered drug targeted at internal tissues. Orally administered drugs must be resistant to the low pH conditions and digestive enzymes present in the gastrointestinal (GI) tract.
To traverse such barriers, drugs targeted at internal tissues are often administered via a transdermal injection, using a syringe and a needle or other mechanical devices. A transdermal injection delivers drugs into the subcutaneous space thus traversing the epidermis-dermis layers.
Anatomically, the skin of a human body is subdivided into three compartments: an epidermis, a dermis and a subcutaneous layer, of which the epidermis plays a key role in blocking drug delivery via the skin (the dourest layer of the epidermis is the stratum corneum which is called also the horny layer). The epidermis is 0.1 mm or more in thickness and consists mainly of protein surrounded by lipid, thus rendering the epidermis hydrophobic.
Although the syringe and needle is an effective delivery device, it is sensitive to contamination, while use thereof is often accompanied by pain and/or bruising. In addition, the use of such a device is accompanied by risk of accidental needle injury to a health care provider.
Mechanical injection devices based on compressed gases have been developed to overcome the above-mentioned limitations of syringe and needle devices. Such devices typically utilize compressed gas (such as, helium or carbon dioxide) to deliver medications at high velocity through a narrow aperture.
Although such devices traverses some of the limitations mentioned above, their efficiency is medication dependent, and their use can lead to pain, bruising and lacerations.
Other less common delivery methods utilize a pulsed Yag laser to punctuate the stratum corneum in order to deliver medication via diffusion and enhancement of ionic compound flux across the skin by the application of an electric current. Although such methods are effective in delivering small charged molecules, a danger of skin burns accompanies their use.
Non-invasive methods, which overcome some of the limitations inherent to the invasive delivery methods described above, have also been described. Such methods utilize preparations, which include an active ingredient disposed within lipid vehicles (e.g., liposomes) or micelles or accompanied with skin permeation agent such that absorption of the active ingredient through the skin is enhanced. Such preparations can be directly applied to a skin region or delivered via transdermal devices such as membranes, pressure-sensitive adhesive matrices and skin patches.
In transdermal delivery, the active ingredient penetrates the skin and enters the capillary blood or the lymph circulation system, which carries the drug to the target organ or to the tissue or has a local effect.
For several years, transdermal drug delivery systems have been employed to effectively introduce a limited number of drugs through unbroken skin. Aside from comfort and convenience, transdermal systems avoid the barriers, delivery rate control problems and potential toxicity concerns associated with traditional administration techniques, such as oral, intramuscular or intravenous delivery.
Although transdermal delivery offers an alternative to some invasive delivery methods, the efficiency thereof is affected by the physical and chemical properties of a drug and physiological or pathological parameters such as the skin hydration, temperature, location, injury, and the body metabolism.
To overcome the limitations of invasive and non-invasive delivery devices, the present inventors propose the use of “stinging cells” (e.g. cnidocytes, nematocytes and the like) or “stinging capsules” (e.g., cnidocysts, nematocysts and polar capsules) isolated therefrom for tissue delivery of a therapeutic or cosmetic agents.
Cnidaria (hydras, sea anemones, jellyfish and corals) are aquatic animals, which possess a variety of compounds which are stored and delivered via specialized capsules (cnidocysts), which form a part of specialized cells termed stinging cells (cnidocytes, nematocytes, ptychocytes and the like). The stinging capsules act as microscopic syringes and serve as a prey or defense mechanism. The Cnidaria family which encompasses 10,000 known species, includes sedentary single or colonial polyps and pelagic jellyfish. In some of these species, cnidocytes account for more than 45% of the cells present (Tardent 1995).
As shown in FIGS. 1a-d, a cnidocyst is a hardened dense capsule, filled with liquid containing a highly folded inverted tubule which sometimes features specialized structures such as shafts, barbs, spines, and/or stylets. In nature, the cnidocyst discharges and releases its tubule (FIG. 1d) into tissue following physical or chemical triggering.
Discharge is initiated by a rapid osmotic influx of water which generates an internal hydrostatic (liquid) pressure of 150 atmospheres forcing capsule rupture and ejection of the tubule (Holstein and Tardent 1984). During ejection, the long coiled and twisted tubule is averted and its length increases by 95 percent. Accelerating at 40,000 g, the tubule untwists to generate a torque force, which rotates the tubule several times around its axis. These mechanical processes generate a powerful driving force, which enables efficient delivery of the compounds, the toxins and enzymes stored within the capsule (Lotan et al. 1995, 1996; Tardent 1995). This process, which occurs within microseconds, is among the most rapid exocytosis events in biology (Holstein and Tardent 1984).
There are at least three dozen known types of cnidocysts (also termed cnidae) including more than 30 varieties of nematocysts found in most Cnidaria and spirocysts, and ptychocysts found mainly in the Cnidaria class Anthozoa (Mariscal 1974).
As is further detailed herein, the present invention utilizes stinging cells such as cnidocytes, or stinging capsules (cnidocysts) isolated therefrom for efficiently delivering agents into a tissue while being devoid of the limitations inherent to prior art invasive or non-invasive delivery devices and compositions.